1. Field of the Art
Embodiments of the present invention generally relate to surgically implanted electronics, in particular, to a ribbon cable that runs through narrow slits in membranes such as the sclera of an eyeball.
2. Description of the Related Art
Age-related macular degeneration (AMD) and retinitis pigmentosa (RP) are two most common outer-retina degenerative diseases of the human eye. There is promise in the use of retinal prostheses in order to allow people afflicted with the diseases to see. Retinal prostheses, which bypass the defective outer-retina photoreceptors and electrically stimulate the inner-retina neurons directly, have allowed some blind people with AMD and RP to perceive light.
It is recognized that these early prostheses only involve a very small number of stimulating electrodes on the neurons. To realize facial recognition or large-sized letter reading, next-generation retinal prosthetic devices may use 1024 or more stimulating electrodes. A 1024-electrode implant can be configured as a 32-by-32 square array of electrodes or with different numbers of electrodes in rectangular, circular, or other shapes.
Around the world, much effort has been put to develop high-density multi-electrode arrays for retinal prosthetic applications. However, even the most advanced prostheses at this time do not have enough stimulating electrodes to restore vision to the desirable functional capability. The simulation results of facial recognition imply that a 1024-electrode retinal implant, with a corresponding number of channels, may be a minimum requirement for blind people to distinguish one from the other.
Stimulating such a large number of electrodes in parallel presents an engineering challenge considering constraints posed by an eyeball. Size, power, heat dissipation, and even buoyancy of electronics are among factors that affect design. Outside the eyeball, an integrated circuit (IC) chip that stimulates the electrodes is less constrained, but getting a thousand plus electrical signals from outside of the eyeball to inside the eyeball—in parallel—is a challenge.
From a surgical point of view, the size of an incision in the sclera of an eye is limited to 3 millimeters (mm) in order to maintain the eyeball's ocular integrity and avoid severe bleeding or inducing retinal detachment. Given a 3-mm wide opening, running 1024 wires in a 3-mm wide flat cable would require a 3-micron (μm) pitch for the wire traces. Pitch includes the width of each conductor (e.g., 1.5 μm) and the width of the gap or insulator between the conductors (e.g., 1.5 μm). Current manufacturing methods have trouble laying down adequate wire traces at a 3-micron pitch on biocompatible polymers such as parylene. And generally, the larger the width of the lines, the more reliably they can be manufactured.
There is a need in the art for improved electronics for surgical implantation.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.